If crime is actually significantly reduced in the United States, what becomes of the prison economy?

&*%$ the prison “economy”! Hopefully, the prison “economy” dies a horrible death. Ideally, the people responsible for the prison “economy”‘s existence and perpetuation would be identified, investigated, and treated as poorly by society and the legal system as the law allows.

Right now the prison system is so over crowded, it would take years to actually make them habitable in the manner they were originally built.
If prisoners weren’t kept in such deplorable conditions, the fighting and murders would be drastically reduced, in my opinion. The prison system could then focus on rehabilitation on those deemed to be able to fit into society. More prisoners could be psychologically evaluated and get the mental help they need.
I went on a tour of a prison here in WV called Moundsville prison. It is closed now. But they had so many prisoners, they were putting 3 to a cell that was 5×7. Two were in the bunk, one in the floor with his face by the toilet. He could’ve moved so that his head was at the bars, but guards would come by and kick them, spit or pee on them.

Here’s a relevant article on the banning of private for profit prisons by some states. I believe there is a bill pending to do so here in NJ.

https://www.vox.com/policy-and-politics/2019/12/1/20989336/private-prisons-states-bans-califonia-nevada-colorado

They might give harsher sentences to minor crimes (and/or misdemeanours)?
Harsher even than the time they give minorities for owning a gram of weed?
Those for-profit prisons don’t run themselves.

This is problematic: the one growth industry defining rural America?

Prisons are not a “growth industry”. They are brutal, hugely inefficient, horrible ways to warehouse people that have problems beyond just their crimes.

Society would be better off, and the economy healthier, if the “prison economy” was eliminated

Hopefully they will be converted into emergency shelters.